Protective circuit for switching transistor - has Zener diode in parallel to transistor base-collector path with lower breakdown voltage than emitter-collector voltage

摘要

The protective circuit is intended for a switching transistor whose emitter-collector path is in series with a high inductance coil. Parallel to the base collector path of the transistor (3) are connected two Zener diodes (7, 8). Their breakdown voltage (UZ) is lower than the permitted emitter-collector voltage (UCE) of the transistor. It is, however, higher than the operating voltage (Ua) effective at the series connection of the transistor and coil (4). This reduces the time required for reduction of the magnetic field of the coil and prevents appearance of undesirable high voltages at the transistor.